Abstract
The effect of tens-of-Watt seed light on the stimulated Raman scattering (SRS) in a distributed side-pumped Yb-doped fiber amplifier is studied. By using two sorts of seed sources with the power smaller than 70 W, it is observed in experiment that the SRS can be enhanced by lowering the seed power. To the best of our knowledge, this is the first observation of the weak-seed enhancement of SRS in the distributed side-pumped Yb-doped fiber amplifier. In order to reveal the physical mechanism of the phenomenon, the numerical study is carried out. It is found that the Yb-gain at Raman wavelength, although much smaller than that at signal wavelength (i.e., 1080 nm), plays an important role in the phenomenon. It is also revealed that the weak-seed enhancement of SRS can only be presented when the dopant concentration is large enough (e.g., larger than 3 × 1025 in our numerical calculation). Besides, with more effective suppression of Raman seed, the weak-seed induced enhancement of SRS could be observed in a larger seed power range. The pertinent results and conclusion can provide significant guidance for designing high-power fiber lasers and amplifiers.
Highlights
High-power Yb-doped fiber lasers and amplifiers have attracted much attention in the last two decades because of their outstanding characteristics such as compactness, robustness, good beam quality and high efficiency [1]–[6], and their wide applications in fields of industrial processing, medicine and scientific research
It is found that the weak-seed enhancement of stimulated Raman scattering (SRS) can be present, and the Yb-gain at the Raman wavelength, is weak, plays an important role in the phenomenon
It revealed that the weak-seed enhancement of SRS can only happen when the dopant concentration is higher enough
Summary
High-power Yb-doped fiber lasers and amplifiers have attracted much attention in the last two decades because of their outstanding characteristics such as compactness, robustness, good beam quality and high efficiency [1]–[6], and their wide applications in fields of industrial processing, medicine and scientific research. Some methods to suppress the negative effect of seed instability were presented, e.g., introducing the long passive fiber in the seed source [16] or optimize the bandwidth of seed source [20] Another seed characteristic is the Raman noisy in the seed light. The seed average power plays an important role in SRS threshold Both the theoretical and experimental studies revealed that the Raman light was proportional to the seed power [12], [20]. In 2019, the SRS threshold of distributed-pumped fiber amplifier was studied analytically and numerically [17], and it was implied that the increment of seed power should lower the SRS threshold. In order to deeply understand the experiment observation, the numerical study is carried out, with the help of which, the pertinent physical mechanism of the weak-seed enhancement of SRS is discussed
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